ABSTRACT Genetic evidence indicates that glia, including microglia and astrocytes, play causal roles in Alzheimer?s disease. Therefore, detailed mechanistic understanding of causal glial factors has strong potential to lead to new therapies. However, little is known about neuronal-glial interactions and how emerging pictures of glial heterogeneity and changing states over time contribute to disease. This proposal aims to define astrocyte subtypes and states present across the spectrum of disease pathology in human neurodegenerative tauopathies, and identify key regulatory factors with which to experimentally manipulate these subtypes and states for mechanistic study, via three specific aims. First, through analyzing a unique single nuclear sequencing dataset to identify diverse astrocyte subtypes and states present across a spectrum of tau pathology and neurodegeneration, and integrating these data with other whole tissue and single cell datasets to identify reproducible findings and observe relationships to other cell types. Second, by identifying and validating key molecular regulators of disease-associated astrocyte subtypes and states by combining bioinformatics predictions with experimental testing in human iPSC models. Third, by assessing the functional relationship between specific astrocytes subtypes and states and neurodegeneration in vivo using mouse models of neurodegeneration. By including both human post-mortem data, experimental human in vitro systems, and mouse in vivo systems, I will focus on robust and reproducible findings that are amenable to detailed functional and mechanistic study. Ensuring the success of this project is a rich institutional environment and mentorship team of world-class leaders in single-cell sequencing, basic astrocyte biology, functional genomics, and experimental disease modeling. The training aspects of this proposal complement a strong background in molecular biology and biochemistry with a solid foundation in genomics and bioinformatics as well as astroglial biology. Altogether, the proposed work completes a professional transition to independent investigator focused on glial mechanisms of neurodegeneration, by establishing the necessary experience and publication record in the integration of functional genomics and single-nuclear sequencing with experimental glia biology.